Digester



Nov.- 11, 1941. A. c. DURDIN, JR

DIGESTER Filed Oct. 19, A1938 2 sheets-sheet 1 ?aienied Nov. l1, 1941 este DIGES'EEB Augustus C. Durdin, Er., Chicago, lll. Application @stolzer 19, 193g, Serial No. 235344 (Cl. 21o- 2) Claims.

This invention relates to digesters and particularly to digesters in which the decomposition of sewage, sludge and other organicA materials is conducted underanaerobic conditions.

Organic decomposition of this type is accompanied by the evolution oi gas of considerable caloriiic value. This gas is normally burned for useful purposes and usually at least some of the eat derived therefrom is utilized for the heating of vthe material being decomposed, since the decomposition is considerably accelerated by reasonably high temperature, of the orderbr" 99 or 196 F.

One of the principal objects of the invention is to provide an improved digester which not only serves to decompose the sludge, but also advantageously serves for the storage of a substantial amount oi gas.

, According to the present invention l prefer to use the body oi the digester .es a receptacle ior e. gas collecting dome. ln or`er to attain this result in a satisfactory manner l have round it necesssary to protect the interior oi the dorne from floating solid material derived from the sludge. Such oating material for some reason or other tends to agglomerate at the surface or the liquid and to coalesce on the apparatus at that level. have found that it does not so coalesce if kept submerged or if lrept in motion.

As will hereinafter be described, the surface upon which such solid materials may oat is reduced to relatively small proportions and such heating solid. material is eectively lrept in motion by diverting the gas produced through said surface, or the material is kept submerged by means which permit the escape of gas upwardly.

The general objects, advantages end capabilities of the invention will readily be understood trom the following description oi three preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which:

Figure l is a vertical section through a digester4 embodying the invention;

Fig. 2 is a similar View through a modified digester embodying the invention, and

Fig. 3 is a similar view through a modiiied digester embodying the invention.

Referring to Fig. 1, my digest/er comprises a basin it which may suitably be built of concrete. This basin may be round, square, or of other suitable shape in cross-section. It is preferably relatively deep and is provided with a hopper bottom il. From its iowermost point extends an outlet pipe ii? controlled by a suitable valveinot shown) so that the mud-like precipitate resulting from the decomposition may be drawn oli" at will. l

Within the 'tank it is a heating coil i3 through which circulates any suitable medium heated by' the combustion of some or al1 of the gas produced by the digester, in well known manner. The tank il? is provided with an inlet pipe lf3 for the introduction or fresh sludge, this inlet being controlled by a suitable valve not shown). rIhe reference numeral it designates a pipe for withdrawal of vthe gas produced. This pipe extends through the wall oi the basin l@ at a low position thereof to a point approximately at the center oi the basin, whence it extends upwardly to a point substantially at the upper level of the basin.

The vertical portion oi the pipe is supported by standard it. it wilh or course, be under stood that the pipe i5 is controlled by a suitable valve or valves lnot shown). For the withdrawal of the clear supernatant liquor l provide a plu rality of pipes il which extend through the wall ci the basin it and terminate within the basin at various levels. The exterior portion or" each pipe il extends upwardly to an overow trough it. This trough is adapted to overilow into a channel it and is arranged so that it' may receive liquid which overflows from the basin it.

'Adjustable weirs i@ and El may be provided to control the level at which overflow may occur. The outer yend of each of the pipes l? is closed by means of a valve t2 which can be opened manually to withdraw supernatant liquor at the draw-oil level of any of the pipes il.

At the suitable position within the lower part of the basin lil l provide a circumferential series of brackets 23 which project for a short distance radially into the basin. These brackets serve as a support for a housing 2t. This housing comprises a substantially cylindrical wall 25, a roof or cover 2t which is preferably domed upwardly toward its center. At its center the roof 26 is provided with a relatively small cylindrical outlet member 2l which extends upwardly above the normal liquid level defined by the weir 2l. The vertical length of the pipe l5 extends upwardly over the outlet El., as seen in Fig. 1.

The housing 2t is slightly smaller than the I basin l@ so as to provide a free annular space- 28 in which the cylindrical skirt 29 of a gas dome 3i) may move freely in accordance with variation of the amount of gas within the dome. It will be noted, vas shown `in Fig. l., that when the gas is withdrawn, the dome st moves downwardly and in its lowest position it is supported by the 55 brackets it.

the pipe i when required.

` liquid is withdrawn by the pipes Il. Any solid 'l material which tends to-iioat moves upwardly 1 into contact with the cover 26, which prevents it 1 from moving to. the surface. Consequently, the

i solid materials are prevented from encrusting on the apparatus and they eventually sink, after being deprived of the gas which buoys them up- Ward. A certain amount ot solid materials ex-L 1 tend into the gas outlet 2 1, but they are maintained in continuous movement by the gas escaping upwardly through this outlet and, consequently, they do not become encrusted on the i surface of the outlet, but become deprived of their gas and sink..

It will be understood that the' digester is operi ated in usual manner, sludge to be digested being 1 introduced periodically by the pipe Il and digested residue being withdrawn periodically by the pipell. The digesting sludge is maintained at a suitable temperature by means of the heat- 1 ing coil I3. During digestion a considerable Vamount oi gasis produced. This gas moves upf wardly into contact with the sloping roof 2t 1 which directs it to the gas outlet 2l. .The gas passes upwardly through this outlet into the dome It. As the gas collects, the dome 30 floats in the liquid in the basin. Gas is withdrawn by In the embodiment of the invention shown in 1 Fig. 2, similar parts have been given similar rei'- erence numerals. In this embodiment the brackets 23 are omitted and the basin il is pro- `vided with an inwardly extending shoulder Ill which serves as a continuum support for a ange 1 32fprovided around the lower edge of the housing 24.

This housing is iirmly anchored to the ledg g 3| by means oi suitable bolts Il. The ledge 8i j also serves as a support f or a gasdome Il when i the sameis in its lower position, as shown in l Fig. 2. This gas dome operates in the annular space 28 between the housing 2i andthe wall of the basinJU. It is to be noted that this aninular space, and if desired also' the annular space above the cover 28, contains sealing water. `These spaces are out of communication with l the space within and below the housing 2l so that initially water has to be provided for the sealing of the gas dome. dees not need to be replaced since a certain amount of condensation normally occurs on the l inner side of the dome and the condensate may f i pass' through an overow Il into a run-oi! trough 35.

The pipes i1 are shown diagramatically as It willreaclily be understood that the digestion process conducted in this apparatus is substanltially similar to Athat described in connection with the embodiment of Fig. 1.

The embodiment of the invention shown in Fig.

consequently, similar reference numerals are apoi' the previously described embodiments is omitted. The gas discharge pipe II passes through anopening in the center of the wall l..

The periorate or foraminous wall 38 may suitably consist oi' a woven screen of appropriate mesh to prevent anyv but the smallest solids i'rom passing through. Thus, I may employ a wire Clear supernatant i wail in the upward direction. Solids tendingto screen of ya" mesh or nner, such as 1,42" or M6" mesh, or a screen of even nner mesh. In some cases, however, I prefer to employ a grille or screen having a larger opening size or mesh.

The operation of this embodiment of the invention is substantially similar to that of the previously'described embodiments. In this embodiment, however, the solids of any substantial size are maintained submerged by the foraminous wallvvll. Gases pass freelythrough this iioat which arestopped by the screen Il become degased and gravitate to the bottom of the digester. It will be noted that the fall oi' the liquid level resulting from the periodic withdrawals of sludge causes a downward iiow of clear liquid through the screen 3l so that any material which tends to collect on the'screen is washed away at frequent intervals and the screen is maintained clear. a

Although the invention has been disclosed in connection with the speciiic details of preferred embodiments thereof, it must be understood 'that such details are ynot intended to be limitative of the invention except in so far as set forth in the accompanying claims.

Having thus described my invention. what I.

claim as new and desire to secure vby Letters Patent oi' the United States is:

l. A digester comprising a tank, means deining a normal liquid level therein, a wall extending transversely of said tank, means maintaining said wall at a xed position below said normal liquid level whereby it is normally submerged in said liquid, a gas collecting inverted bell adapted to be gas iloated in said tank, said inverted bell Ordinarly this water being controlled by valves 30, which valves may '1 be located at any desired position.

3 islargely similar to that shown in Fig. 2 and,

having a skirt extending downwardly into the liquid space between the rst said wall and -the ywall of the tank. said transverse wall having pertorations therein to permit upward passage of gas while preventing large solids from moving upwardly into contact with the interior of said bell, means for supplying material to said tank, means for withdrawing material from said tank, and means for withdrawing gas from said inverted bell above said liquid level.

2. A digester comprising a tank, means deilning a normal liquid level therein, a drum, means maintaining said drum normally submerged within said tank below said liquid level, the side wall of the drum being in spaced relation to said tank.

a gas collecting inverted bell adapted to be gas iiostedin said tank around the said drum, the

upper end o! said drum being of screen material to permit upward passage of gas while preventing large solids from moving upwardly into contact with said gas collecting inverted bell, means i'or supplying material to said tank, means for withdrawing material tromsaid tank. and meansl tor withdrawing gas from said gas collecting inverted bell above said liquid lev 3. A digester comprising a tank, means denning a normal liquid level' therein, an impervious wall extending transversely of said tank, means maintaining said wall normally submerged at a iixed position below said level, said wall terminating short oi the tank wall, a gas outlet ex.- tending upwardly from iirst said wall to a posi-v aseasve tion above said level, a gas collecting inverted bell adapted to be gas floated in said tank, said inverted bell having a skirt extending downwardly into the liquid space between the first said wall and the wall of the tank, means for supplying material to said tank, means for withdrawing material from said tank, and means for withdrawing gas from said inverted bell above said liquid level.

4. A digester comprising a tank, means denning a maximum liquid'level therein, an inverted bell, means maintaining said bell in a fixed position and normally submerged within said tank below said liquid level and located in spaced relation to the Wall of said tank, said bell having a gas outlet extending upwardly to a. position above said liquid level, a' gas collecting inverted bell adapted to be gas floated in said tank,'last said bell having a skirt extending downwardly into the liquid space between the iirst said bell and the wall of the tank, means for supplying material to said tank, means for withdrawing material from said tank, and means for withdrawing gas from said gas collecting inverted bell above said liquid level.

5. A disasterV comprising a tank, means denning a maximum liquid level therein, supporting means at an intermediate height in said tank, an inverted bell suppord in said tank by said supporting means in a position below said liquid level, said bell extending into close propinduity and in spaced relation to the wall of the tank, said bell having a gas outlet extending upwardly to a position above said liquid level, an inverted gas collecting bell adapted to be gas floated; in s aid tank, said collecting bell having a skirt extending downwardly into the space between said bell and the wall of the tank, means for supplying material to said tank, means for withdrawing material fromsaid tank, and means'for withdrawing gas from said gas collecting inverted bell above said liquid level.

6. A digester comprising a tank, means denning a mum liquid level therein, an inverted bell 'supported in said tank in a. position below said liquid level, said bell extending into close and spaced relation to the wall of the tank. means supporting said bell and establishing liquldftlht relation with the wall of the tank to provide an annular space around said bell adapted to contain liquid separated from the liquid in the main portion of the tank. said bell having a gas outlet extending upwardly to a position above said liql uid level, a gas collecting inverted bell adapted to be gas oated in liquid in said annular space,

means for supplying material to said tank, means for withdrawing material from lsaid tank, and means for withdrawing gas from said gas collecting inverted bell above said liquid level.

'1. A digester comprising a tank, means denning a maximum liquid level therein, the wall of the tank being provided with a ledge at a position below said liquid level, an inverted bell within said tank in a position below said liquid level, said bell being supported upon and being sealed to said ledge and being arranged'in close and spaced relation to the wall of the tank above said ledge, said bell has a gas outlet extending up wardly to s. position'above said liquid level, a gas lcollecting bell adapted to be gas floated in liquid in the annular space between the rst said bell and the tank wall, last said bell being suprted wall in its lowest position,`means for sup-` material to d means for. withdrew s material from said tank, and means for withdrawing ses from said gas collecting inverted bell above said liquid level.

a. A disaster compaia a tank, means deilnins a 1. i liduid level therein, an open d supported in said tank in a ypcniitlon below said liquid level, said drum exten into close.

and seed relation to the wall of the tank, me supporting said and establish liquidtiglit relation with said wall of than tanks to provide an 1 space around said i screen material enclos the upperk wall of said drum whereby solid 'materials are maintained submerged, we ses is permitted to upwardly,

a gas collec bell adapted to be gas nested in said alas space, means for supplyins material f; said means for withdrawins material f i cli-ss gas from said inverted bell above said AUGUSTUS C. DURDIN, Jn.

' liquid level.

a.; said tank, and mea for witn- 

